Jave_TreeSet_Comparable

1：Person类中重写compareTo()函数

class Person implements Comparable<Person> {
    public String name;
    public int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public int compareTo(Person o) {
        return this.age - o.age;
    }
    @Override
    public String toString () {
        return this.age + " " + this.name;
    }
}

static void test12() {
        TreeSet<Person> ts = new TreeSet<>();
        Person p1 = new Person("小明", 19);
        Person p2 = new Person("小红", 10);
        Person p3 = new Person("小军", 12);
        ts.add(p1);
        ts.add(p2);
        ts.add(p3);
        for (Person i : ts) {
            System.out.println(i.toString());
        }
    }

结果： 

10 小红
12 小军
19 小明

2：调用次数较少或只用一次时，写匿名函数

static void test13() {
        TreeSet<Person> ts = new TreeSet<Person>(
                new Comparator<Person>() {
                    @Override
                    public int compare(Person o1, Person o2) {
                        return o1.age - o2.age;
                    }
                }
        );
        Person p1 = new Person("小明", 19);
        Person p2 = new Person("小红", 10);
        Person p3 = new Person("小军", 18);
        ts.add(p1);
        ts.add(p2);
        ts.add(p3);
        for (Person i : ts) {
            System.out.println(i.toString());
        }
    }

结果：

10 小红
12 小军
19 小明

3：创建Comparator接口的实现类，然后调用带参构造传入该类的对象com

class AgeCom implements Comparator<Person> {
    @Override
    public int compare(Person o1, Person o2) {
        return o1.age - o2.age;
    }
}

static void test14() {
        Comparator<Person> com = new AgeCom();
        TreeSet<Person> ts = new TreeSet<Person>(com);
        Person p1 = new Person("小明", 19);
        Person p2 = new Person("小红", 10);
        Person p3 = new Person("小军", 12);
        ts.add(p1);
        ts.add(p2);
        ts.add(p3);
        for (Person i : ts) {
            System.out.println(i.toString());
        }
    }

结果：

10 小红
12 小军
19 小明